Tear film mucins: front line defenders of the ocular surface; comparison with airway and gastrointestinal tract mucins

Differential Diagnosis of Sjögren Versus Non-Sjögren Dry Eye Through Tear Film Biomarkers

PURPOSE

Systemic implications necessitate the identification of dry eye patients with Sjögren syndrome (SS). This study aims to explore the utility of tear MUC5AC and inflammatory cytokine levels in the differential diagnosis of SS-related dry eye.

METHODS

A prospective, observational, case-control study was conducted on 62 patients (those with a definitive diagnosis of SS dry eye, non-SS dry eye, and age-matched healthy controls with no dry eye). Clinical evaluations included the following tests in the order listed here: noninvasive tear break-up time, osmolarity, tear sampling, Schirmer test without anesthesia, and ocular surface staining (lissamine green for conjunctiva and fluorescein for cornea). Tear MUC5AC levels were assessed with enzyme-linked immunosorbent assay, and cytokines [interferon-gamma, tumor necrosis factor alpha, interleukin (IL)-6, IL-17a, IL-1β, IL-8, IL-10, and IL-12p70] were measured using a Luminex assay in a masked fashion.

RESULTS

The Bulbar conjunctival lissamine green staining score was significantly greater in patients or controls with SS versus non-SS dry eye. This greater conjunctival staining was associated with a reduction in tear MUC5AC (B = -17.8 ng/mL, 95% confidence interval = -31.8 to -3.9, P = 0.01). Among the tear cytokines, a significant association was found between IL-8 levels (hazard ratio [HR] = 1.002, 95% confidence interval = 1.000-1.003, P = 0.03) and SS diagnosis. When patients were stratified based on tear MUC5AC levels, significantly increased tear IL-8 levels were detected in patients with SS dry eye but not with non-SS dry eye, in comparison with healthy controls.

CONCLUSIONS

Tear levels of goblet cell-specific MUC5AC combined with IL-8 can potentially serve as a useful biomarker for differential diagnosis of SS dry eye from non-SS dry eye.

Role of Choline in Ocular Diseases

Choline is essential for maintaining the structure and function of cells in humans. Choline plays an important role in eye health and disease. It is a precursor of acetylcholine, a neurotransmitter of the parasympathetic nervous system, and it is involved in the production and secretion of tears by the lacrimal glands. It also contributes to the stability of the cells and tears on the ocular surface and is involved in retinal development and differentiation. Choline deficiency is associated with retinal hemorrhage, glaucoma, and dry eye syndrome. Choline supplementation may be effective for treating these diseases.

Optimization of goblet cell density quantification methods

The purpose of this study was to develop a standardized, accurate and efficient method for estimating conjunctival goblet cell density (GCD) via optimizing sample storage conditions and quantification methods. Conjunctival impression cytology (CIC) membranes were collected from both eyes of 32 participants and were randomized to two storage durations (2-3 weeks, 6-7 weeks) and two storage container types (microcentrifuge tube, flat histology cassette). The CIC membranes were stained and subdivided into 25 areas (5 mm × 5 mm) for imaging and the GCs were counted under 200X magnification using three different methods: (1) full CIC membrane GC count of the 25 images with cell-counting software ("full"; reference method), (2) partial membrane GC count of 9 images with cell-counting software ("partial"), and (3) manual counting of the 25 images ("manual"). In all cases, GCD was determined by dividing the GC count by the counting area. The average time required for quantification was recorded to gauge efficiency. Results showed no significant difference in GC count between the two storage durations (p = 0.745) or storage container types (p = 0.552). The median (interquartile range (IQR)) time required to quantify a CIC membrane for the full, partial, and manual methods of GC counting, was 14.8(17.6), 4.6(5.2) and 5.0 (5.0) minutes, respectively. The agreement of GCD values between the full and manual methods (bias: 0.4, 95% LOA: [-4.6, 5.5]) was stronger than that comparing the full and partial methods (bias: 0.5, 95% LOA: [-18, 17]). All together, through systematic examination of key procedural variables, an optimized method for GCD quantification within 7 weeks of sample collection was outlined. Adaption of procedures described in this paper to facilitate accurate and efficient GCD quantification may serve as a valuable step in clinical trials investigating DED pathophysiology and/or novel DED treatment strategies.

Inducing dry eye disease using a custom engineered desiccation system: Impact on the ocular surface including keratin-14-positive limbal epithelial stem cells

PURPOSE

Dry eye disease (DED) is characterized by loss of tear film stability that becomes self-sustaining in a vicious cycle of pathophysiological events. Currently, desiccation stress (DS) is the dominant procedure for inducing DED in mice, however its' effect on limbal epithelial stem cells (LESCs) has been overlooked. This study aimed to establish a DS model via the use of a novel hardware to investigate the impact on the ocular surface including LESCs.

METHODS

A mouse transporter unit was customized to generate a dehumidified environment. C57BL/6J mice were exposed to mild DS and injected with scopolamine hydrobromide (SH) or remained untreated (UT) under standard vivarium conditions for 10 consecutive days (n = 28/group). Clinical assessments included phenol red tear-thread test, fluorescein staining and optical coherence tomography assessments. Histopathological and immunofluorescence was used to evaluate tissue architecture, goblet cell (GC) status, lacrimal gland (LG) inflammation and epithelial phenotype on the ocular surface. Whole flat-mounted corneas were immunostained for keratin-14 (K14), then imaged by confocal microscopy and analyzed computationally to investigate the effect of DS on LESCs.

RESULTS

Custom modifications made to the animal transporter unit resulted in dehumidified cage relative humidity (RH) of 43.5 ± 4.79% compared to the vivarium 53.9 ± 1.8% (p = 0.0243). Under these conditions, aqueous tear production in mice was suppressed whilst corneal permeability and corneal irregularity significantly increased. H&E staining indicated stressed corneal basal epithelial cells and increased desquamation. DS-exposed mice had reduced GC density (41.0 ± 5.10 GC/mm vs 46.9 ± 3.88 GC/mm, p = 0.0482) and LGs from these mice exhibited elevated CD4⁺ cell infiltration compared to controls. DS elicited K14⁺ epithelial cell displacement, as indicated by increased fluorescence signal at a distance of 50-100 μm radially inwards from the limbus [0.63 ± 0.053% (DS) vs 0.54 ± 0.060% (UT), p = 0.0317].

CONCLUSIONS

Application of mild DS using customized hardware and SH injections generated features of DED in mice. Following DS, ocular surface epithelial cell health decreased and LESCs appeared stressed. This suggested that potential downstream effects of DS on corneal homeostasis are present, a phenomenon that is currently under-investigated. The method used to induce DED in this study enables the development of a chronic model which more closely resembles disease seen in the clinic.

Pro-Resolving Mediator Annexin A1 Regulates Intracellular Ca2+ and Mucin Secretion in Cultured Goblet Cells Suggesting a New Use in Inflammatory Conjunctival Diseases

The amount of mucin secreted by conjunctival goblet cells is regulated to ensure the optimal level for protection of the ocular surface. Under physiological conditions lipid specialized pro-resolving mediators (SPM) are essential for maintaining tissue homeostasis including the conjunctiva. The protein Annexin A1 (AnxA1) can act as an SPM. We used cultured rat conjunctival goblet cells to determine if AnxA1 stimulates an increase in intracellular [Ca²⁺] ([Ca²⁺]_i) and mucin secretion and to identify the signaling pathways. The increase in [Ca²⁺]_i was determined using fura2/AM and mucin secretion was measured using an enzyme-linked lectin assay. AnxA1 stimulated an increase in [Ca²⁺]_i and mucin secretion that was blocked by the cell-permeant Ca²⁺ chelator BAPTA/AM and the ALX/FPR2 receptor inhibitor BOC2. AnxA1 increased [Ca²⁺]_i to a similar extent as the SPMs lipoxin A₄ and Resolvin (Rv) D1 and histamine. The AnxA1 increase in [Ca²⁺]_i and mucin secretion were inhibited by blocking the phospholipase C (PLC) pathway including PLC, the IP₃ receptor, the Ca²⁺/ATPase that causes the intracellular Ca²⁺ stores to empty, and blockade of Ca²⁺ influx. Inhibition of protein kinase C (PKC) and Ca²⁺/calmodulin-dependent protein kinase also decreased the AnxA1-stimulated increase in [Ca²⁺]_i and mucin secretion. In contrast inhibitors of ERK 1/2, phospholipase A₂ (PLA₂), and phospholipase D (PLD) did not alter AnxA1-stimulated increase in [Ca²⁺]_i, but did inhibit mucin secretion. Activation of protein kinase A did not decrease either the AnxA1-stimulated rise in [Ca²⁺]_i or secretion. We conclude that in health, AnxA1 contributes to the mucin layer of the tear film and ocular surface homeostasis by activating the PLC signaling pathway to increase [Ca²⁺]_i and stimulate mucin secretion and ERK1/2, PLA₂, and PLD to stimulate mucin secretion from conjunctival goblet cells.

Corneal collagen as a potential therapeutic target in dry eye disease

Dry eye disease (DED) is a major cause of ocular discomfort, inflammation and dysfunction worldwide. Tear film instability in DED both causes and is exacerbated by disruption of the corneal epithelium. This tandem leads to a cycle of inflammation at the corneal surface involving immune cell dysregulation and increased chemokines and cytokines, which activate mitogen-activated protein kinases in the epithelium and elevates matrix metalloproteinases (MMPs). We review evidence suggesting that corneal collagen might be highly susceptible in DED to MMP-induced disruption, digestion, and thinning. We also summarize that collagen is far from inert and contains binding sites that serve as ligands for multiple inflammatory and immune regulators. Fragmented collagen not only challenges these receptor-ligand binding relationships, but also can promote recruitment and motility of pro-inflammatory immune cells. Current physician-directed therapies for DED focus on reducing inflammation, but do not directly ameliorate the underlying corneal damage that could exacerbate surface inflammation. We argue that an important gap in practice is lack of a direct therapeutic reparative for damaged corneal collagen, which is slow to heal, and likely amplifies sight-threatening inflammation. Healing fragmented collagen in the cornea may represent a more effective means to interrupt the "vicious cycle" of inflammation in DED and other conditions that damages, sometimes irreversibly, the ocular surface.

Review of Approaches for Increasing Ophthalmic Bioavailability for Eye Drop Formulations

Ophthalmic diseases represent a significant problem as over 2 billion people worldwide suffer from vison impairment and blindness. Eye drops account for around 90% of ophthalmic medications but are limited in success due to poor patient compliance and low bioavailability. Low bioavailability can be attributed to short retention times in the eye caused by rapid tear turnover and the difficulty of drug diffusion through the multi-layered structure of the eye that includes lipid-rich endothelial and epithelial layers as well as the stroma which is high in water content. In addition, there are barriers such as tight junctional complexes in the corneal epithelium, lacrimal turnover, nasolacrimal drainage, blinking reflexes, efflux transporters, drug metabolism by ocular enzymes, and drug binding to or repulsion from conjunctival mucins, tear proteins, and melanin. In order to maximize transport through the cornea while minimizing drug loss through other pathways, researchers have developed numerous methods to improve eye drop formulations including the addition of viscosity enhancers, permeability enhancers, mucoadhesives, and vasoconstrictors, or using formulations that include puncta occlusion, nanocarriers, or prodrugs. This review explains the mechanism behind each of these methods, examines their history, analyzes previous and current research, evaluates future applications, and discusses the pros and cons of each technique.

Liposomes as vehicles for topical ophthalmic drug delivery and ocular surface protection

Introduction: The development of ophthalmic formulations able to deliver hydrophilic and hydrophobic drugs to the inner structures of the eye and restore the preocular tear film has been a leading topic of discussion over the last few years. In this sense, liposomes represent a suitable strategy to achieve these objectives in ocular drug delivery.Areas covered: Knowledge of the different physiological and anatomical eye structures, and specially the ocular surface are critical to better understanding and comprehending the characteristics required for the development of topical ophthalmic liposomal formulations. In this review, several features of liposomes are discussed such as the main materials used for their fabrication, basic structure and preparation methods, from already established to novel techniques, allowing the control and design of special characteristics. Besides, physicochemical properties, purification processes and strategies to overcome delivery or encapsulation challenges are also presented. Expert opinion: Regarding ocular drug delivery of liposomes, there are some features that can be redesigned. Specific biocompatible and biodegradable materials presenting therapeutic properties, such as lipidic compounds or polymers significantly change the way of tackling ophthalmic diseases. Besides, liposomes entail an effective, safe and versatile strategy for the treatment of diseases in the clinical practice.

Mouse Models of Sjögren's Syndrome with Ocular Surface Disease

Sjögren’s syndrome (SS) is a systemic rheumatic disease that predominantly affects salivary and lacrimal glands resulting in oral and ocular dryness, respectively, referred to as sicca symptoms. The clinical presentation of ocular dryness includes keratoconjunctivitis sicca (KCS), resulting from the inflammatory damage to the ocular surface tissues of cornea and conjunctiva. The diagnostic evaluation of KCS is a critical component of the classification criteria used by clinicians worldwide to confirm SS diagnosis. Therapeutic management of SS requires both topical and systemic treatments. Several mouse models of SS have contributed to our current understanding of immunopathologic mechanisms underlying the disease. This information also helps develop novel therapeutic interventions. Although these models address glandular aspects of SS pathology, their impact on ocular surface tissues is addressed only in a few models such as thrombospondin (TSP)-1 deficient, C57BL/6.NOD.Aec1Aec2, NOD.H2^b, NOD.Aire KO, and IL-2Rα (CD25) KO mice. While corneal and/or conjunctival damage is reported in most of these models, the characteristic SS specific autoantibodies are only reported in the TSP-1 deficient mouse model, which is also validated as a preclinical model. This review summarizes valuable insights provided by investigations on the ocular spectrum of the SS pathology in these models.

Glaucoma: Management and Future Perspectives for Nanotechnology-Based Treatment Modalities

Glaucoma, being asymptomatic for relatively late stage, is recognized as a worldwide cause of irreversible vision loss. The eye is an impervious organ that exhibits natural anatomical and physiological barriers which renders the design of an efficient ocular delivery system a formidable task and challenge scientists to find alternative formulation approaches. In the field of glaucoma treatment, smart delivery systems for targeting have aroused interest in the topical ocular delivery field owing to its potentiality to oppress many treatment challenges associated with many of glaucoma types. The current momentum of nano-pharmaceuticals, in the development of advanced drug delivery systems, hold promises for much improved therapies for glaucoma to reduce its impact on vision loss. In this review, a brief about glaucoma; its etiology, predisposing factors and different treatment modalities has been reviewed. The diverse ocular drug delivery systems currently available or under investigations have been presented. Additionally, future foreseeing of new drug delivery systems that may represent potential means for more efficient glaucoma management are overviewed. Finally, a gab-analysis for the required investigation to pave the road for commercialization of ocular novel-delivery systems based on the nano-technology are discussed.

Poroelasticity of highly confined hydrogel films measured with a surface forces apparatus

The influence of poroelasticity on the contact mechanics of thin polyacrylamide films was investigated with a surface forces apparatus (SFA). A model based on a thin film approximation described compression forces for hydrated gels; polymer scaling theory explained the effects of gel dehydration. The results demonstrate that fluid flow dictates the apparent stiffness of highly confined poroelastic films.

Why Chain Length of Hyaluronan in Eye Drops Matters

The chain length of hyaluronan (HA) determines its physical as well as its physiological properties. Results of clinical research on HA eye drops are not comparable without this parameter. In this article methods for the assessment of the average molecular weight of HA in eye drops and a terminology for molecular weight ranges are proposed. The classification of HA eye drops according to their zero shear viscosity and viscosity at 1000 s-1 shear rate is presented. Based on the gradient of mucin MUC5AC concentration within the mucoaqueous layer of the tear film a hypothesis on the consequences of this gradient on the rheological properties of the tear film is provided. The mucoadhesive properties of HA and their dependence on chain length are explained. The ability of HA to bind to receptors on the ocular epithelial cells, and in particular the potential consequences of the interaction between HA and the receptor HARE, responsible for HA endocytosis by corneal epithelial cells is discussed. The physiological function of HA in the framework of ocular surface homeostasis and wound healing are outlined, and the influence of the chain length of HA on the clinical performance of HA eye drops is illustrated. The use of very high molecular weight HA (hylan A) eye drops as drug vehicle for the next generation of ophthalmic drugs with minimized side effects is proposed and its advantages elucidated. Consequences of the diagnosis and treatment of ocular surface disease are discussed.

Effects of Aqueous-Supplementing Artificial Tears in Wearers of Biweekly Replacement Contact Lenses vs Wearers of Daily Disposable Contact Lenses

PURPOSE

To compare the effects of artificial tears (ATs) in wearers of biweekly replacement silicone hydrogel contact lenses (BW-Ws) and wearers of daily disposable contact lenses (DD-Ws) of the same material.

MATERIALS AND METHODS

The aqueous-supplementing ATs, OPTOyalA and OPTOidro, were assigned to be used for 2 weeks to healthy and young subjects: 1) 20 (8 and 12, respectively) BW-Ws wearing silicone hydrogel somofilcon A CLs (Clariti Elite), 2) 18 (9 and 9, respectively) DD-Ws wearing silicone hydrogel somofilcon A CLs (Clarity 1 Day), and 3) a control group of 33 (16 and 17, respectively) N-Ws. Ocular symptoms and comfort, tear volume and stability, and ocular surface condition were assessed by Ocular Surface Disease Index (OSDI), 5-Item Dry Eye Questionnaire (DEQ5), tear meniscus height (TMH), non-invasive tear break-up time (NIBUT), and evaluation of ocular redness (OR). The assessment was performed before and after 15 days of use of the ATs in the 3 groups (BW-Ws, DD-Ws, and N-Ws).

RESULTS

No clear significant difference was noted in symptoms and signs between OPTOyalA and OPTOidro irrespectively of the group of people studied. ATs use for 15 days produced a significant improvement in DEQ5 and OR in DD-Ws (Δ=-34%, p=0.006; Δ=-23%, p<0.001) and in N-Ws (Δ=-21%, p=0.001; Δ=-10%, p=0.006) but not in BW-Ws (Δ=-5%, p=0.072; Δ=-2%, p=0.257). No significant change was noted for TMH.

CONCLUSION

In young and healthy subjects, the aqueous-supplementing effect of the ATs under consideration is more a rinsing and tear replacem ent effect than an increase in tear volume, and it produces an improvement of the eye redness and ocular symptoms. Contact lens wear influenced the effectiveness of ATs in a way which is correlated with the CL replacement schedule.

Highly Transparent Covalent Mucin Coatings Improve the Wettability and Tribology of Hydrophobic Contact Lenses

A stable, good coverage of the corneal tissue by the tear film is essential for protecting the eye. Contact lenses, however, constitute a foreign body that separates the tear film into two thinner layers, which are then more vulnerable toward disruption. This effect is even more pronounced if the contact lenses possess an insufficient surface wettability, which, in addition to friction, is suggested to be linked to discomfort and damage to the ocular surface. In this study, we establish covalent surface coatings with mucin macromolecules to overcome this issue for pure silicone contact lenses. This material class, which outperforms state-of-the-art silicone hydrogels in terms of oxygen permeability, is not yet used for commercial contact lens applications, which is due to its strongly hydrophobic surface characteristics. The applied process stably attaches a transparent mucin layer onto the contact lenses and thereby establishes hydrophilic surfaces that not only prevent lipid adsorption but also interact very well with liquid environments. Most importantly, however, we show that those mucin coatings are indeed able to prevent wear formation on corneal tissue that is subjected to the tribological stress applied by a contact lens. Our results open up great possibilities for a variety of hydrophobic materials that are, to date, not suitable for a contact lens application. Furthermore, the ability of mucin coatings to reduce wear in a tissue/synthetic material contact might be also beneficial for other biomedical applications.

Maresin 1, a specialized proresolving mediator, stimulates intracellular [Ca2+ ] and secretion in conjunctival goblet cells

Mucin secretion from conjunctival goblet cells forms the tear film mucin layer and requires regulation to function properly. Maresin 1 (MaR1) is a specialized proresolving mediator produced during the resolution of inflammation. We determined if MaR1 stimulates mucin secretion and signaling pathways used. Cultured rat conjunctival goblet cells were used to measure the increase in intracellular Ca²⁺ ([Ca^{2 +} ]_i ) concentration and mucin secretion. MaR1-increased [Ca²⁺ ]_i and secretion were blocked by inhibitors of phospholipase C, protein kinase C, Ca²⁺ /calmodulin-dependent protein kinase II, and extracellular-regulated kinase 1/2. MaR1 added before addition of histamine counterregulated histamine-stimulated increase in [Ca²⁺ ]_i and secretion. We conclude that MaR1 likely has two actions in conjunctival goblet cells: first, maintaining optimal tear film mucin levels by increasing [Ca²⁺ ]_i and stimulating mucin secretion in health and, second, attenuating the increase in [Ca²⁺ ]_i and overproduction of mucin secretion by counterregulating the effect of histamine as occurs in ocular allergy.

RvE1 uses the LTB4 receptor BLT1 to increase [Ca2+]i and stimulate mucin secretion in cultured rat and human conjunctival goblet cells

PURPOSE

Specialized pro-resolving lipid mediator resolvin (Rv) E1 stimulates secretion including mucins from conjunctival goblet cells. RvE1 can use both its ChemR23 receptor and the LTB₄ receptor BLT1 to increase [Ca²⁺]_i. The purpose of this study was to determine the expression of ChemR23 and BLT1 and receptors on conjunctival goblet cells and the respective roles these two receptors play in goblet cell responses to RvE1.

METHODS

Goblet cells were cultured from male rat or human conjunctiva from both sexes. Western blotting analysis, reverse transcription PCR and immunofluorescence microscopy were used to demonstrate the expression of ChemR23 and BLT1 in conjunctival goblet cells. High molecular weight glycoprotein secretion was determined using an enzyme-linked lectin assay. Signaling pathways were studied by measuring the increase in [Ca²⁺]_i using fura 2/AM.

RESULTS

ChemR23 and BLT1 and receptors were present on both rat and human conjunctival goblet cells. The BLT1 inhibitors LY293111 and U75302 significantly blocked RvE1-and LTB₄-stimulated [Ca²⁺]_i increase. RvE1-and LTB₄-stimulated [Ca²⁺]_i and secretion increases were blocked by BLT1-targeted siRNA. RvE1-stimulated [Ca²⁺]_i and secretion increases were also blocked by ChemR23-targeted siRNA. Addition of RvE1 2 min before or simultaneously with LTB₄ desensitized the LTB₄ [Ca²⁺]_i response. Addition of RvE1 and LTB₄ simultaneously caused secretion that was decreased compared to either response alone.

CONCLUSION

RvE1, in addition to the ChemR23 receptor, uses the BLT1 receptor to increase [Ca²⁺]_i and stimulate secretion in both rat and human cultured conjunctival goblet cells.

Graft Versus Host Disease-Associated Dry Eye: Role of Ocular Surface Mucins and the Effect of Rebamipide, a Mucin Secretagogue

Purpose

The present study was designed to investigate the role of ocular surface glycocalyx and mucins in graft versus host disease (GVHD)-associated dry eye. The ameliorative effect of topical rebamipide, a mucin secretagogue, on GVHD-associated dry eye was also tested.

Methods

A mouse model of allogeneic transplantation was used to induce ocular GVHD with C57BL/6 as donors and B6D2F1 as recipient mice. Phenol red thread method and fluorescein staining was used to quantify tear secretion and corneal keratopathy. At 8 weeks after the allogeneic transplantation, corneas were harvested to perform glycocalyx staining and confocal microscopy. Goblet cell staining was performed using periodic acid Schiff's staining. Corneal and tear film levels of Mucin 1, 4, 16, 19, and 5AC were quantified using ELISA and real-time PCR. Rebamipide was applied topically twice daily to mice eyes.

Results

Allogeneic transplantation resulted in ocular GVHD-associated dry eye characterized by a significant decrease in tear film volume and the onset of corneal keratopathy. Ocular GVHD caused a significant decrease in the area and thickness of corneal glycocalyx. A significant decrease in the goblet cells was also noted. A significant decrease in mucin 4 and 5AC levels was also observed. Topical treatment with rebamipide partially attenuated ocular GVHD-mediated decrease in tear film volume and significantly reduced the severity of corneal keratopathy.

Conclusions

Ocular GVHD has detrimental impact on ocular surface glycocalyx and mucins. Rebamipide, a mucin secretagogue, partially prevents ocular GVHD-associated decrease in tear film and reduces the severity of corneal keratopathy.

Histological and immunohistochemical characterization of the porcine ocular surface

The ocular surface of the white domestic pig (Sus scrofa domestica) is used as a helpful model of the human ocular surface; however, a complete histological description has yet to be published. In this work, we studied porcine eyeballs with intact eyelids to describe and characterize the different structures that form the ocular surface, including the cornea and conjunctiva that covers the bulbar sclera, tarsi, and the nictitating membrane. We determined the distribution of goblet cells of different types over the conjunctiva and analyzed the conjunctival-associated lymphoid tissue (CALT). Porcine eyeballs were obtained from a local slaughterhouse, fixed, processed, and embedded in paraffin blocks. Tissue sections (4 μm) were stained with hematoxylin/eosin, Alcian blue/Periodic Acid Schiff, and Giemsa. Slides were also stained with lectins from Arachis hypogaea (PNA) and Helix pomatia (HPA) agglutinins and immunostained with rabbit anti-CD3. We found that the porcine cornea was composed of 6–8 epithelial cell layers, stroma, Descemet’s membrane, and an endothelial monolayer. The total corneal thickness was 1131.0±87.5 μm (mean±standard error of the mean) in the center and increased to 1496.9±138.2 μm at the limbus. The goblet cell density was 71.25±12.29 cells/mm, ranging from the highest density (113.04±37.21 cells/mm) in the lower palpebral conjunctiva to the lowest density (12.69±4.29 cells/mm) in the bulbar conjunctiva. The CALT was distributed in the form of intraepithelial lymphocytes and subepithelial diffuse lymphoid tissue. Lenticular-shaped lymphoid follicles, about 8 per histological section, were also present within the conjunctival areas. In conclusion, we demonstrated that the analyzed porcine ocular structures are similar to those of humans, confirming the potential usefulness of pig eyes to study ocular surface physiology and pathophysiology.

Engineered metal oxide nanomaterials inhibit corneal epithelial wound healing in vitro and in vivo

Ocular exposure to metal oxide engineered nanomaterials (ENMs) is common as exemplified by zinc oxide (ZnO), a major constituent of sunscreens and cosmetics. The ocular surface that includes the transparent cornea and its protective tear film are common sites of exposure for metal ENMs. Despite the frequency of exposure of the ocular surface, there is a knowledge gap regarding the effects of metal oxide ENMs on the cornea in health and disease. Therefore, we studied the effects of metal oxide ENMs on the cornea in the presence or absence of injury. Cell viability of immortalized human corneal epithelial (hTCEpi) cells was assessed following treatment with 11 metal oxide ENMs with a concentration ranging from 0.5 to 250 μg/mL for 24 hours. An epithelial wound healing assay with a monolayer of hTCEpi cells was then performed using 11 metal oxide ENMs at select concentrations based on data from the viability assays. Subsequently, based on the in vitro results, in vivo testing of precorneal tear film (PTF) quantity and stability as well as a corneal epithelial wound healing were tested in the presence or absence ZnO or vanadium pentoxide (V₂O₅) at a concentration of 50 μg/mL. We found that WO₃, ZnO, V₂O₅ and CuO ENMs significantly reduced hTCEpi cell viability in comparison to vehicle control or the other metal oxide ENMs tested. Furthermore, ZnO and V₂O₅ ENMs also significantly decreased hTCEpi cell migration. Although ZnO and V₂O₅ did not alter PTF parameters of rabbits in vivo, corneal epithelial wound healing was significantly delayed by topical ZnO while V₂O₅ did not alter wound healing. Finally, hyperspectral images confirmed penetration of ZnO and V₂O₅ through all corneal layers and into the iris stroma. Considering the marked epithelial toxicity and corneal penetration of ZnO, further investigations on the impact of this ENM on the eye are warranted.

Meibomian gland dysfunction (MGD), as diagnosed by non-contact infrared Meibography, in dogs with ocular surface disorders (OSD): a retrospective study

Background

Meibomian gland dysfunction (MGD) is one of the possible conditions underlying ocular surface disorders (OSD). Prevalence of MGD in dogs affected by OSD has not yet been reported. We aimed to evaluate the prevalence of MGD among OSD canine patients, which had been assessed by non-contact infrared meibography and interferometry, and to identify MGD associated factors that might guide its diagnosis. Medical records of canine patients examined for OSD between 2016 and 2019 were reviewed. The frequency of MGD was evaluated within different categories (skull conformation, gender, eye and STT-1). The putative MGD risk factors and frequency of MGD within grades of interferometry were evaluated in a regression analysis model and reported as odd ratios (ORs).

Results

One hundred fifty eyes from 81 dogs with OSD were included with median age 75 months (range 3–192) and female representation with 52%. MGD was present in 70% of the examined eyes. MGD risk was higher in males OR_adj = 3.015 (95% CI: 1.395–6.514) (P = 0.005) and older patients OR_adj = 1.207 (95% CI: 1.081–1.348) (P = 0.001). No significant differences were found between left and right eyes (P = 0.66) or between the two types of skull conformation (P = 0.477) and MGD presence. MGD was associated to the lowest lipid layer (LL) thickness, as assessed by interferometry (grade 0) OR = 16.00 (95% CI: 2.104–121.68) (P < 0.001). STT values were not significantly associated with the presence of MGD (P > 0.05).

Conclusions

MGD is a common underlying pathology in OSD. Being male and higher age are risk factors for MGD. An interferometry grade 0 may guide OSD diagnosis towards MGD.

Occupational effect of sugarcane biomass burning on the conjunctival mucin profile of harvest workers and residents of an adjacent town - A Brazilian panel study

Pre-harvest burning of sugarcane fields produces large amounts of air pollutants which are known to cause health problems, including ocular surface abnormalities. In this study, we evaluated the effect of biomass burning on mucus quality and mucin gene expression (MUC1, MUC5AC, MUC16) in the conjunctiva of sugarcane workers (SWs) and residents of an adjacent town (RTs). Impression cytology samples of the inferior tarsal and bulbar conjunctiva of 78 SWs and 32 RTs were collected before (T1) and immediately after (T2) a 6-month harvest period. The neutral, acid and total mucus content of goblet cells was determined by PAS and AB staining. The levels of MUC5AC, MUC1 and MUC16 mRNA in the conjunctiva were measured by real-time PCR. Compared to RTs, SWs had higher levels of bulbar acid mucus and MUC16 mRNA and tarsal MUC5AC mRNA at T2 and lower levels of neutral mucus at T1 and T2. In the SW group, MUC1 mRNA levels were higher at T2 than at T1, but the levels of neutral and acid mucus were similar. In the RT group, acid mucus decreased and neutral mucus increased in the bulbar and tarsal conjunctiva at T2. In conclusion, our findings show that sugarcane harvesting is associated with abnormalities in mucus quality and content and changes in mucin mRNA levels on the ocular surface. This may help explain the ocular inflammatory signs and symptoms observed in subjects exposed to air pollutants and high temperatures from sugarcane biomass burning.

Structural and Molecular Tear Film Changes in Glaucoma

The Tear Film (TF) is a trilaminar and dynamic fluid covering the entire Ocular Surface (OS), consisting of a mucus, aqueous, and lipid layer deeply interacting between them. Because of its structure and functions, TF plays a pivotal role in the preservation of the OS integrity and the quality of vision. Medical therapy for glaucoma is recognized to profoundly disturb the OS homeostasis by altering all components of the ocular surface unit, including TF. The presence of preservatives, the number of daily eye drops instillations, and the duration of therapy are the main contributors to TF changes. From the physio-pathological side, TF alterations are induced by toxic and allergic mechanisms and result from goblet cell and Meibomian gland loss, dysfunction of accessory lacrimal glands, and epithelial disruption. In detail, TF changes are represented by mucus layer thinning, reduced mucin concentration, aqueous layer volume reduction, and lipid layer thinning with increased tear evaporation. Hyper- osmolarity and instability represent the main hallmarks of these changes and are an expression of a iatrogenic form of dry eye. TF undergoes also molecular modifications that primarily reflect a therapy- or disease-induced inflammatory status of the OS. Over the last years, this field of research aimed a progressively growing interest since molecular variations may be considered as potential candidate biomarkers of glaucoma. The aim of this review is to report the main TF changes occurring during glaucoma, exploring the relationship they may have with the glaucoma-related ocular surface disease and the patient quality of life, and their utility as potential biomarkers of disease.

The Important Role of the Chemokine Axis CCR7-CCL19 and CCR7-CCL21 in the Pathophysiology of the Immuno-inflammatory Response in Dry Eye Disease

Purpose: To explore whether CCR7-CCL19 and CCR7-CCL21 affect the pathophysiology of the dry eye disease (DED) immuno-inflammatory response using a murine model.Methods: The mRNA expression levels of CCR7, CCL19, CCL21 and VEGF-C within corneas in DED mice were detected by real-time PCR. Immunofluorescence and flow cytometric analyses were performed to mark dendritic cells (DCs) and detect correlations among CCR7, CCL19, CCL21 and lymphatic vessels.Results: CCR7, CCL19 and CCL21 expression was dramatically increased during the development of DED. In addition, CCR7, which is expressed in DCs, was located inside and around lymphatic vessels and colocalized with CCL19 or CCL21. Positive correlations were observed between CCR7 and CCL19 (P < .01, r = 0.862), CCL21 (P < .01, r = 0.759), and VEGF-C (P < .05, r = 0.607).Conclusions: Our study revealed that both the CCR7-CCL19 and CCR7-CCL21 chemokine axis are important for DC migration to lymphatic vessels, but CCL19 may have a greater effect on DED than CCL21.

Achyranthis radix Extract Improves Urban Particulate Matter-Induced Dry Eye Disease

Dry eye disease (DED) is a multifactorial inflammatory disease that severely impairs patients' quality of life. Particulate matter comprises a harmful mixture of particles less than 10 μm in size, which on contact with the eye, causes inflammation in the cornea/conjunctival epithelium, threatening eye health and triggering the onset of DED. Achyranthis radix is an ingredient of traditional medicine generally used for treating osteoporosis, trauma, and thrombosis in Asian countries. However, the effect of Achyranthis radix on eye health has not been elucidated. In this study, we evaluate the protective effect of Achyranthis radix hot water extract (ARE) in a rat model of urban particulate matter (UPM)-induced DED. UPM with or without ARE were topically administered on both eyes thrice daily for 10 days. ARE induced tear secretion and improved corneal irregularity. Additionally, ARE treatment protected the corneal epithelial cells from UPM-induced apoptosis. It also restored rMuc4 expression in the cornea and increased goblet cell density in the conjunctiva. These results are suggestive of the potential of ARE as a topical therapeutic agent for treating DED.

A New Ophthalmic Pharmaceutical Formulation, Topical Sulglycotide, Enhances the Ocular Mucin Secretion in Desiccation Stress-Mediated Dry Eye Disease

Purpose

The aim of this study was the investigation of the effect of sulglycotide (SOS), a polysulfated glycopeptide derived from porcine duodenal mucin, for the treatment of dry eye disease.

Methods

NOD.B10.H2b mice were exposed to an air draft for 10 days, and, simultaneously, scopolamine hydrobromide was injected subcutaneously. The mice were randomly divided into nine groups as follows: four kinds of SOS formulations and three kinds of commercial medicine. After 10 days of treatment, we estimated the effect of treatment on tear production, epithelium stabilization, mucin secretion, and inflammation.

Results

The desiccation stress significantly decreased tear production and corneal epithelium stabilization, as well as markedly decreased the numbers of goblet cells and mucin-stained cells in conjunctiva. However, the topical 4% SOS eye drops markedly increased tear production and corneal stabilization, which recovered to baseline levels. In addition, topical 4% SOS significantly induced an increase in the numbers of goblet cells and the expression of membrane-associated mucins including MUC1, MUC4, and MUC16, as well as the gel-forming mucin, MUC5AC. Furthermore, SOS formulations provided anti-inflammatory improvement in a dose-dependent manner.

Conclusions

In summary, we suggest that a new ophthalmic pharmaceutical formulation, topical sulglycotide, enhances the ocular mucin secretion in dry eye disease and can be used as a new ophthalmic pharmaceutical material to treat dry eye disease.

Conjunctival Microbiome-Host Responses Are Associated With Impaired Epithelial Cell Health in Both Early and Late Stages of Trachoma

Background: Trachoma, a neglected tropical disease, is the leading infectious cause of blindness and visual impairment worldwide. Host responses to ocular chlamydial infection resulting in chronic inflammation and expansion of non-chlamydial bacteria are hypothesized risk factors for development of active trachoma and conjunctival scarring.

Methods: Ocular swabs from trachoma endemic populations in The Gambia were selected from archived samples for 16S sequencing and host conjunctival gene expression. We recruited children with active trachoma and adults with conjunctival scarring, alongside corresponding matched controls.

Findings: In children, active trachoma was not associated with significant changes in the ocular microbiome. Haemophilus enrichment was associated with antimicrobial responses but not linked to active trachoma. Adults with scarring trachoma had a reduced ocular bacterial diversity compared to controls, with increased relative abundance of Corynebacterium. Increased abundance of Corynebacterium in scarring disease was associated with innate immune responses to the microbiota, dominated by altered mucin expression and increased matrix adhesion.

Interpretation: In the absence of current Chlamydia trachomatis infection, changes in the ocular microbiome associate with differential expression of antimicrobial and inflammatory genes that impair epithelial cell health. In scarring trachoma, expansion of non-pathogenic bacteria such as Corynebacterium and innate responses are coincident, warranting further investigation of this relationship. Comparisons between active and scarring trachoma supported the relative absence of type-2 interferon responses in scarring, whilst highlighting a common suppression of re-epithelialization with altered epithelial and bacterial adhesion, likely contributing to development of scarring pathology.

[Pathogenesis and epidemiology of neurotrophic keratopathy]

Neurotrophic keratopathy (NK) is a degenerative corneal disease that is based on an impairment of the corneal innervation. The damage to the sensory innervation, which is delivered through the 1st branch of the trigeminal nerve (ophthalmic nerve), can occur throughout the entire length of the nerve from the nucleus in the brainstem, e.g. caused by brain tumors, to the terminal nerve fibers in the cornea, caused for example by refractive corneal surgery (e. g. LASIK). Due to the loss of the sensory innervation, a reduced lacrimation and a reduction in the secretion of trophic factors occur. This in turn inhibits the regeneration potential of the corneal epithelium. In the most severe cases of the disease, the reduction or loss of lacrimation, together with the impaired regeneration potential of the epithelial cells, can lead to persistent epithelial defects, ulcers and corneal perforation. The NK has a prevalence of 5 or fewer individuals per 10,000 and is classified as a rare, i. e. orphan disease (ORPHA137596). A fundamental understanding of the pathogenesis and epidemiology of NK supports the early diagnosis and therefore the initiation of a specific treatment.

Pathophysiological Role and Drug Modulation of Calcium Transport in Ocular Surface Cells

The ocular surface structure and extraocular accessory organs constitute the ocular surface system, which includes the cornea, conjunctiva, eyelids, lacrimal organs, and lacrimal passages. This system is composed of, and stabilized by, the corneal epithelium, conjunctival cells, conjunctival goblet cells, lacrimal acinar cells and Tenon's fibroblasts, all of which maintain the healthy eyeball surface system. Ocular surface diseases are commonly referred to corneal and conjunctival disease and external ocular disease, resulting from damage to the ocular surface structure. A growing body of evidence has indicated that abnormal activation of the KCa3.1 channel and Ca2+/ calmodulin-dependent kinase initiates ocular injury. Signaling pathways downstream of the irregular Ca2+ influx induce cell progression and migration, and impair tight junctions, epithelial transport and secretory function. In this overview, we summarize the current knowledge regarding ocular surface disease in terms of physical and pathological alteration of the ocular system. We dissect in-depth, the mechanisms underlying disease progression, and we describe the current calcium transport therapeutics and the obstacles that remain to be solved. Finally, we summarize how to integrate the research results into clinical practice in the future.

The Effect of Rebamipide Ophthalmic Solution on Cytokine and Mucin Secretion in Culture of Conjunctival Epithelial Cells From the Cu, Zn-Superoxide Dismutase-1 (SOD-1) Knock-Down Mouse

OBJECTIVES

To evaluate the in vitro effects of 1-mM rebamipide ophthalmic solution on the expression of inflammatory cytokines and MUC5AC in Cu, Zn-superoxide dismutase-1 (SOD-1) knock-down conjunctival epithelium.

METHODS

Conjunctival epithelium from C57BL/6 wild-type mice was cultured and treated with rebamipide ophthalmic solution. Using cytometric bead array, we examined the levels of interleukin-(IL)-6, IL-10, IL-17, monocyte chemoattractant protein-1, interferon-γ (INF-γ), tumor necrosis factor, and IL-12p70 in the culture supernatants. The culture supernatants were obtained from the culture medium of nontreated or SOD-1 knock-down conjunctival epithelium using small interfering RNA (siRNA). In addition, ELISA was performed to ascertain the MUC5AC concentration in the culture medium.

RESULTS

After rebamipide ophthalmic solution was applied, IL-6 concentration in the supernatants of conjunctival epithelial cells treated with and without siRNA showed a significant timewise decrease from 0 to 24 hr (963±42 to 0.07±0.05 pg/mL and 932±168 to 2.2±0.05 pg/mL, respectively) (P<0.001). Compared with baseline values, MUC5AC concentrations significantly increased 24 hr after rebamipide application to the conjunctival cultures-both with and without SOD-1 siRNA treatment (P<0.05 in both cases).

CONCLUSIONS

Rebamipide seems to increase MUC5AC levels and suppress inflammation by decreasing IL-6 levels in mouse conjunctival epithelial cell cultures. SOD-1 siRNA-treated mouse conjunctival epithelial cell culture is a practical method for investigating changes in mucosa-associated mucins and proinflammatory cytokines in response to therapeutic interventions.

Therapeutic implications of nanomedicine for ocular drug delivery

Delivering therapeutics to the eye is challenging on multiple levels: rapid clearance of eyedrops from the ocular surface requires frequent instillation, which is difficult for patients; transport of drugs across the blood-retinal barrier when drugs are administered systemically, and the cornea when drugs are administered topically, is difficult to achieve; limited drug penetration to the back of the eye owing to the cornea, conjunctiva, sclera and vitreous barriers. Nanomedicine offers many advantages over conventional ophthalmic medications for effective ocular drug delivery because nanomedicine can increase the therapeutic index by overcoming ocular barriers, improving drug-release profiles and reducing potential drug toxicity. In this review, we highlight the therapeutic implications of nanomedicine for ocular drug delivery.

Stromal Fibroblasts Drive Host Inflammatory Responses That Are Dependent on Chlamydia trachomatis Strain Type and Likely Influence Disease Outcomes

Chlamydia trachomatis ocular strains cause a blinding disease known as trachoma. These strains rarely cause urogenital infections and are not found in the upper genital tract or rectum. Urogenital strains are responsible for a self-limited conjunctivitis and the sequelae of infertility, ectopic pregnancy, and hemorrhagic proctitis. However, the differential cellular responses that drive these clinically observed disease outcomes are not completely understood. Primary conjunctival, endocervical, and endometrial epithelial and stromal fibroblast cells, HeLa229 cells, and immortalized conjunctival epithelial (HCjE) cells were infected with the ocular A/Har-13 (A) and Ba/Apache-2 (Ba) strains and urogenital D/UW-3 (D) and E/Bour (E) strains. Infection rates, progeny production, and cytokine/chemokine secretion levels were evaluated in comparison with those in uninfected cells. All strain types infected all cell types with similar levels of efficacy and development. However, progeny production levels differed among primary cells: Ba produced significantly more progeny than E in endocervical and endometrial fibroblasts, while A progeny were less abundant than E progeny. C.trachomatis infection of primary epithelial cells elicited an increase in pro- and anti-inflammatory mediators compared to levels in uninfected cells, but there were no significant differences by strain type. In contrast, for primary fibroblasts, ocular strains elicited significant increases in the pro- and anti-inflammatory mediators macrophage inflammatory protein (MIP)-1β, thymus- and activation-regulated chemokine (TARC), interleukin (IL)-2, IL-12p70, and interferon gamma-induced protein 10 (IP-10) compared to levels in urogenital strains, while urogenital strains elicited a distinct and significant increase in the proinflammatory mediators IL-1α, IL-1β, IL-8, gamma interferon (IFN-γ), and granulocyte-macrophage colony-stimulating factor (GM-CSF). Our data indicate that primary fibroblasts, not epithelial cells, drive host inflammatory responses that are dependent on strain type and likely influence disease outcomes, establishing their importance as a novel model for studies of C. trachomatis disease pathogenesis.IMPORTANCEChlamydia trachomatis is a human pathogen and the leading cause of preventable blindness and sexually transmitted diseases in the world. Certain C. trachomatis strains cause ocular disease, while others cause upper genital tract pathology. However, little is known about the cellular or immunologic basis for these differences. Here, we compared the abilities of the strain types to infect, replicate, and initiate an immune response in primary human ocular and urogenital epithelial cells, as well as in fibroblasts from the underlying stroma. While there were no significant differences in infection rates or intracellular growth for any strain in any cell type, proinflammatory responses were driven not by the epithelial cells but by fibroblasts and were distinct between ocular and urogenital strains. Our findings suggest that primary fibroblasts are a novel and more appropriate model for studies of immune responses that will expand our understanding of the differential pathological disease outcomes caused by various C. trachomatis strain types.

Functional Consequences of Keratan Sulfate Sulfation in Electrosensory Tissues and in Neuronal Regulation

Keratan sulfate (KS) is a functional electrosensory and neuro-instructive molecule. Recent studies have identified novel low sulfation KS in auditory and sensory tissues such as the tectorial membrane of the organ of Corti and the Ampullae of Lorenzini in elasmobranch fish. These are extremely sensitive proton gradient detection systems that send signals to neural interfaces to facilitate audition and electrolocation. High and low sulfation KS have differential functional roles in song learning in the immature male zebra song-finch with high charge density KS in song nuclei promoting brain development and cognitive learning. The conductive properties of KS are relevant to the excitable neural phenotype. High sulfation KS interacts with a large number of guidance and neuroregulatory proteins. The KS proteoglycan microtubule associated protein-1B (MAP1B) stabilizes actin and tubulin cytoskeletal development during neuritogenesis. A second 12 span transmembrane synaptic vesicle associated KS proteoglycan (SV2) provides a smart gel storage matrix for the storage of neurotransmitters. MAP1B and SV2 have prominent roles to play in neuroregulation. Aggrecan and phosphacan have roles in perineuronal net formation and in neuroregulation. A greater understanding of the biology of KS may be insightful as to how neural repair might be improved.

Investigating the Effects of Stove Emissions on Ocular and Cancer Cells

More than a third of the world’s population relies on solid fuels for cooking and heating, with major health consequences. Although solid fuel combustion emissions are known to increase the prevalence of illnesses such as chronic obstructive pulmonary disease and lung cancer, however, their effect on the eyes is underexplored. This study assesses the acute toxicity of solid fuel combustion emissions on healthy ocular cells and a cancer cell line. Three healthy ocular cell lines (corneal, lens, and retinal epithelial cells) and a cancer cell line (Chinese hamster ovary cells) were exposed to liquid and gas phase emissions from applewood and coal combustion. Following the exposure, real-time cell attachment behavior was monitored for at least 120 hours with electrical cell impedance spectroscopy. The viability of the cells, amount of apoptotic cells, and generation of reactive oxygen species (ROS) were quantified with MTT, ApoTox-Glo, and ROS-Glo H₂O₂ assays, respectively. The results showed that coal emissions compromised the viability of ocular cells more than applewood emissions. Interestingly, the cancer cells, although their viability was not compromised, generated 1.7 to 2.7 times more ROS than healthy cells. This acute exposure study provides compelling proof that biomass combustion emissions compromise the viability of ocular cells and increase ROS generation. The increased ROS generation was fatal for ocular cells, but it promoted the growth of cancer cells.

Immunoresolvent Resolvin D1 Maintains the Health of the Ocular Surface

The present review focuses on the role of one of the D-series resolvins (Rv) RvD1 in the regulation of conjunctival goblet cell secretion and its role in ocular surface health. RvD1 is the most thoroughly studied of the specialized proresolution mediators in the goblet cells. The anterior surface of the eye consists of the cornea (the transparent central area) and the conjunctiva (opaque tissue that surrounds the cornea and lines the eyelids). The secretory mucin MUC5AC produced by the conjunctival goblet cells is protective of the ocular surface and especially helps to maintain clear vision through the cornea. In health, a complex neural reflex stimulates goblet cell secretion to maintain an optimum amount of mucin in the tear film. The specialized pro-resolution mediator, D-series resolvin (RvD1) is present in human tears and induces goblet cell mucin secretion. RvD1 interacts with its receptors ALX/FPR2 and GPR32, activates phospholipases C, D, and A2, as well as the EGFR. This stimulation increases the intracellular [Ca2+] and activates extracellular regulated kinase (ERK) 1/2 to cause mucin secretion into the tear film. This mucin secretion protects the ocular surface from the challenges in the external milieu thus maintaining a healthy interface between the eye and the environment. RvD1 forms a second important mechanism along with activation of a neural reflex pathway to regulate goblet cell mucin secretion and protect the ocular surface in health.

Resolvin D1 treatment on goblet cell mucin and immune responses in the chronic allergic eye disease (AED) model

Severe, chronic eye allergy is an understudied, vision-threatening condition. Treatments remain limited. We used a mouse model of severe allergic eye disease (AED) to determine whether topical application of the pro-resolution mediator Resolvin D1 (RvD1) terminates the response. AED was induced by injection of ovalbumin (OVA) followed by topical challenge of OVA daily. RvD1 was applied topically prior to OVA. Clinical symptoms were scored. Eye washes were assayed for MUC5AC. After 7 days, eyes were removed and the number of goblet cells, T helper cell responses and presence of immune cells in draining lymph nodes and conjunctiva determined. Topical RvD1 treatment significantly reduced symptoms of AED. RvD1 did not alter the systemic type 2 immune response in the lymph nodes. AED increased the total amount of goblet cell mucin secretion, but not the number of goblet cells. RvD1 prevented this increase, but did not alter goblet cell number. Absolute numbers of CD4 + T cells, total CD11b + myeloid cells, eosinophils, neutrophils, and monocytes, but not macrophages increased in AED versus RvD1-treated mice. We conclude that topical application of RvD1 reduced the ocular allergic response by local actions in conjunctival immune response and a decrease in goblet cell mucin secretion.

Reconsidering the central role of mucins in dry eye and ocular surface diseases

Mucins are key actors in tear film quality and tear film stability. Alteration of membrane-bound mucin expression on corneal and conjunctival epithelial cells and/or gel-forming mucin secretion by goblet cells (GCs) promotes in ocular surface diseases and dry eye disease (DED). Changes in the mucin layer may lead to enhanced tear evaporation eventually contributing to tear hyperosmolarity which has been associated with ocular surface inflammation. Inflammatory mediators in turn may have a negative impact on GCs differentiation, proliferation, and mucin secretion. This sheds new light on the position of GCs in the vicious circle of DED. As contributor to ocular surface immune homeostasis, GC loss may contribute to impaired ocular surface immune tolerance observed in DED. In spite of this, there are no tools in routine clinical practice for exploring ocular surface mucin deficiency/dysregulation. Therefore, when selecting the most appropriate treatment options, there is a clear unmet need for a better understanding of the importance of mucins and options for their replacement. Here, we comprehensively revisited the current knowledge on ocular surface mucin biology, including functions, synthesis, and secretion as well as the available diagnostic tools and treatment options to improve mucin-associated homeostasis. In particular, we detailed the potential link between mucin dysfunction and inflammation as part of the uncontrolled chronic inflammation which perpetuates the vicious circle in DED.

[Gel-forming mucins structure governs mucus gels viscoelasticity]

Mucus is the first line of innate mucosal defense in all mammals. Gel‑forming mucins control the rheological properties of mucus hydrogels by forming a network in which hydrophilic and hydrophobic regions coexist, and it has been revealed that the network is formed through both covalent links and reversible links such as hydrophobic interactions in order to modulate the structure as a function of the physiological necessities. Here, we review the structure and functions of the mucus in terms of the gel-forming mucins protein-protein interactions, also called interactome. Since it is difficult to characterize the low energy reversible interactions due to their dependence on physico-chemical environment, their role is not well understood. Still, they constitute a promising target to counteract mucus abnormalities observed in mucus-associated diseases.

Volcanic ash from Puyehue-Cordón Caulle Volcanic Complex and Calbuco promote a differential response of pro-inflammatory and oxidative stress mediators on human conjunctival epithelial cells

Volcanic ash could pose a hazard to the ocular surface as it is constantly exposed to environmental particles. We exposed conjunctival cells to Puyehue-Cordón Caulle volcanic complex (PCCVC) or Calbuco ash particles and evaluated proliferation, viability, apoptosis, MUC1 expression, pro-inflammatory cytokines, and oxidative stress markers. Ash particles from these volcanoes vary in size, composition, and morphology. Our results demonstrate that PCCVC but not Calbuco ash particles induce cytotoxicity on human conjunctival epithelial cells viewed as a decrease in cell proliferation and the transmembrane mucin MUC1 expression; a pro-inflammatory response mediated by IL-6 and IL-8; and an imbalance of the redox environment leading to protein oxidative damage. This is the first in vitro study that assesses the biological effect of volcanic ash particles on human conjunctival epithelial cells and the involvement of inflammatory mediators and oxidative stress as the mechanisms of damage. Our results could provide a better understanding of the ocular symptoms manifested by people living near volcanic areas.

Insights into gold nanoparticles as a mucoadhesive system

A large number of drugs are administered on different mucosal surfaces. However, due to the poor mucoadhesion of the current formulations, their bioavailability is often very low. The development of efficient mucoadhesive drug delivery systems is thus crucial for improving the performance of these drugs. The mucoadhesive properties of gold nanoparticles were investigated. First, two types of gold nanoparticles were synthesized: AuNP1 and AuNP2. AuNP1 only contain internal thiol groups on their metallic core, and AuNP2 contain both internal and peripheral thiol groups. Different protocols based on an adapted quantitative colorimetric method, UV-visible and fluorescence spectroscopies were then developed to gather information on their mucoadhesive properties. Moreover, a global correction factor for the inner filter effect in spectrofluorimetry was proposed, and the data obtained were compared to those commonly used in the literature. Mucins deeply interact with AuNP1, perturbing their core, whereas they remain at the periphery of AuNP2. The quantitative method suggests that a larger number of mucins interact with AuNP2. The establishment of this protocol could be applied to assess the mucoadhesive properties of other stable molecules. This mucoadhesive property of gold nanoparticles could be combined with their drug delivery ability in order to improve the medication administered on mucosa.

Stability of allergens

For proteins to cause IgE-mediated allergic reactions, several common characteristics have to be defined, including small molecular size, solubility and stability to changing pH levels and enzymatic degradation. Nevertheless, these features are not unique for potent allergens, but are also observed in non-allergenic proteins. Due to the increasing awareness by regulatory authorities regarding the allergy pandemic, definition of characteristics unique to potent allergens would facilitate allergenicity assessment in the future. Despite major research efforts even to date the features unique for major allergens have not been elucidated so far. The route of allergen entry into the organism determines to a great extent these required characteristics. Especially orally ingested allergens are exposed to the harsh milieu of the gastrointestinal tract but might additionally be influenced by food processing. Depending on molecular properties such as disulphide bonds contributing to protein fold and formation of conformational IgE epitopes, posttranslational protein modification or protein food matrix interactions, enzymatic and thermal stability might differ between allergens. Moreover, also ligand binding influences structural stability. In the current review article, we aim at highlighting specific characteristics and molecular pattern contributing to a stabilized protein structure and overall allergenicity.

Development of In Vitro Methodologies to Investigate Binding by Sodium Hyaluronate in Eye Drops to Corneal Surfaces

PURPOSE

To develop in vitro methods to assess binding by sodium hyaluronate in eye drops to corneal surfaces.

METHODS

Two different, complementary corneal binding set-ups were developed. In a dynamic in vitro model, confluent corneal epithelial cells (HCE-T) were assembled in chamber slides and a declining channel. A static model was constructed with ex vivo porcine corneas clamped in Franz cells. To test the predictive capacity of models, four different eye drops containing sodium hyaluronate were spiked with tritium-labeled sodium hyaluronate to standardize quantification. In both settings, eye drops were applied for 5 min and physiological conditions were mimicked by flushing with artificial tear fluid. Spreading experiments on HCE-T next to synthetic membranes were used for further characterization.

RESULTS

Binding was more pronounced in dynamic HCE-T model. Three of the four eye drops demonstrated sigmoidal elution of sodium hyaluronate, suggesting pronounced binding. One solution eluted distinctly faster, likewise the buffer control. The static method produced a similar ranking but at lower levels. When eye drops in which phosphate buffer was replaced by citrate buffer (i.e., to prevent calcification) were used, binding was not influenced. All eye drops spread immediately when placed on HCE-T and at the same order of magnitude on glass and polyethylene terephthalate surfaces.

CONCLUSION

Dynamic and static models performed on different corneal sources were used to determine sodium hyaluronate binding kinetics in solutions under physiological conditions. These methodologies resulted in a ranking of the capacity of sodium hyaluronate to bind in vitro to corneal surfaces.

Efficacy of polyethylene glycol-propylene glycol-based lubricant eye drops in reducing squamous metaplasia in patients with dry eye disease

Purpose

Squamous metaplasia in dry eye disease (DED) manifesting as the loss of conjunctival goblet cells results in reduced mucin secretion and tear film instability. The objective of this study was to evaluate the efficacy of a polyethylene glycol–propylene glycol/hydroxypropyl-guar (PEG-PG/HP-guar) artificial tear formulation in reducing the squamous metaplasia in patients with DED using conjunctival impression cytology (CIC).

Methods

In this Phase IV, single-arm, open-label study, DED patients (aged ≥18 years) with a corneal staining sum score ≥3 and tear film break-up time (TFBUT) <7 s self-administered the PEG-PG/HP-guar artificial tears, 3 times a day for a period of 90 days. The primary end point was the change from baseline in goblet cell density (Nelson’s CIC grading score) over the treatment period. Other end points were change in the corneal and conjunctival staining scores, and TFBUT. Statistical evaluation was performed using a paired t-test.

Results

In total, 49 patients (n=98 eyes) completed the study. Compared with baseline, there was a significant reduction in the mean CIC scores (ie, improvement in goblet cell density) at Days 30, 60, and 90 (1.6±0.5 vs 1.2±0.5, 0.9±0.5, and 0.8±0.5; P<0.0001). At Day 90, 22% of eyes demonstrated squamous metaplasia Grade 0 (ie, normal epithelium). Similar improvements were observed in the corneal staining scores (5.7 vs 3.1, 1.1, and 0.5; P<0.0001), conjunctival staining scores (5.5 vs 3.6, 1.6, and 0.9; P<0.0001), and TFBUT (4.8 vs 5.8, 6.3, and 6.8 s; P<0.0001) at Days 30, 60, and 90, respectively.

Conclusion

In this study, treatment with PEG-PG/HP-guar artificial tears for 90 days decreased CIC score, reduced corneal and conjunctival staining, and increased TFBUT in patients with DED. These results suggest that PEG-PG/HP-guar artificial tears can improve the ocular surface health and reverse the changes induced by squamous metaplasia in DED.

Evolutionary conservation of the antimicrobial function of mucus: a first defence against infection

Mucus layers often provide a unique and multi-functional hydrogel interface between the epithelial cells of organisms and their external environment. Mucus has exceptional properties including elasticity, changeable rheology and an ability to self-repair by re-annealing, and is therefore an ideal medium for trapping and immobilising pathogens and serving as a barrier to microbial infection. The ability to produce a functional surface mucosa was an important evolutionary step, which evolved first in the Cnidaria, which includes corals, and the Ctenophora. This allowed the exclusion of non-commensal microbes and the subsequent development of the mucus-lined digestive cavity seen in higher metazoans. The fundamental architecture of the constituent glycoprotein mucins is also evolutionarily conserved. Although an understanding of the biochemical interactions between bacteria and the mucus layer are important to the goal of developing new antimicrobial strategies, they remain relatively poorly understood. This review summarises the physicochemical properties and evolutionary importance of mucus, which make it so successful in the prevention of bacterial infection. In addition, the strategies developed by bacteria to counteract the mucus layer are also explored.